Computerized mapping systems have been developed to search for, identify, and discover information about geographic locations. One form of such computerized mapping systems includes travel-planning Internet websites. With an excess of 50 million unique monthly users, such map sites are a very popular offering. Examples of such sites include AOL's MapQuest, Yahoo's Telcontar-based maps, and Microsoft's MapPoint.net suite. Such sites all work along the lines of a common model, as will now be described.
When a Web user asks for a new map view (e.g., by entering a postal address, or by clicking a navigation link next to a current map view), the user's Web browser sends to a Web server a request indicating the boundaries of the new map view. The Web server in turn extracts the corresponding vector-based map data from a database, and draws a bitmap image of the map. The server then converts the bitmap to an image format supported by the user's Web browser and returns the image, sometimes embedded in HTML, to the user's Web browser so that it can be displayed. Other map Web sites, such as Britain's MultiMaps or Australia's WhereIs utilize a raster-based map database instead. In these cases, it is not necessary to extract vectors and draw a map image. Rather, these functions are replaced by simply extracting the appropriate part of a larger, pre-rendered image.
Whether vector-based or raster-based, such existing map systems are typically engaged using computer systems having substantial memory capacity (e.g., hard disk and RAM), such as desk top and laptop computers. Currently, such computers generally have unconstrained resources (e.g., substantial processing power and memory combined with broadband network/Internet connections), for the purposes of efficiently engaging a digital mapping system. However, it is also desirable to engage such mapping systems from mobile devices, such as cell phones, satellite phones, and personal digital assistants (PDAs).
Currently, such devices typically do not have enough memory to store an entire atlas for one country or even one region. Even if they did possess such capabilities, it is unclear how such a large dataset would be downloaded to a memory, or if a user would wish to do so. Building a mapping application for a cell phone requires downloading map images on an as-needed basis. However, current mobile networks are both slow and suffer from high-latency (e.g., 500-1000 ms latency, 2-4 KB/s throughput). In addition, many wireless carriers (e.g., cellular services) require users to pay per byte. Thus, downloading map images to mobile devices is generally constrained, particularly with conventional mapping systems.
What is needed, therefore, are techniques that enable users to access and use digital mapping systems with constrained-resource services and/or devices.